The present invention relates to acoustical control media which can be formed in panels or the like for use in noise reduction.
There exists a great variety of acoustical material used, in for example, sound absorbing panels forming room dividers in offices, ceiling tile, and the like. The existant structure typically relies on either the sound absorptive properties of a very low density typically fiberglass material useful in absorbing higher frequency components of undesired noise. Frequently, in connection with such fill materials, solid barriers also are employed for blocking high and low frequency energy. High density perforated surface material has been employed also and in some cases in combination with cellular chambers to provide resonant cavities at the audible spectrum for absorbing lower frequency components of acoustical energy. Representative of such prior art are U.S. Pat. Nos. 3,132,714; 3,166,149; 3,211,253; 3,384,199; 3,448,823; 3,502,171; 3,712,846; 3,949,827; 4,155,211. A discussion of the mathematical principles associated with perforated panels is provided in an article entitled "Sound Absorption by Structures with Perforated Panels" by Jacques Brillouin, published in Sound and Vibration in July 1968.
Although the prior art structures provide noise reduction at either the upper or lower end of the frequency spectrum and some efforts have been made to broaden the bandwidth of the sound absorptive or controlling properties of acoustical panels employing for example a combination of techniques, existant structure has not provided the degree of noise isolation desirable in modern offices in which room dividing acoustical panels are employed to divide an office space into individual work areas. In this environment, a relatively small decible change in noise reduction provides a significant increase in privacy for the work areas. Typically to improve low frequency attenuation the thickness of a given sound absorptive panel is increased. It is desirable however to provide as thin an acoustical panel as possible to conserve space as well as provide an aesthetically pleasing appearance.